Unity 5 uv bug?

EDIT: Don't blame me for the bad coding, it's just for testing purposes :P

So I've tried to solve this on my own but I've had no luck so far.
And since no one else seems to have this issue, I doubt it's a bug.

What I'm simply doing is build a mesh from script and apply a texture to it. I've done that many times before.

The problem now is that I have always 6 triangles in my mesh that are completely black. And they are always at world position 0,0,0.

Even if I move my mesh, the black triangles stay at 0,0,0.

The meshes origin is always at 0,0,0. I just change the the vertices position to move the mesh.

I've tried a custom and the standard shader. Same effect on both.

If someone wants to see the script. The relevant code should be in BuildMesh().

 using UnityEngine;
 using System.Collections.Generic;
 
 public class TerrainLayer : MonoBehaviour {
 
     public static int TERRAIN_WIDTH = 16;
     public static int TERRAIN_HEIGHT = 9;
 
     public Vector3 position;
 
     private byte[] terrainData;
     private Mesh mesh;
 
     public bool rebuildMesh;
 
     private float textureUnit = 0.0625f;
     private float textureMargin = 0.0001f;
     private List<Vector3> vertices;
     private List<int> triangles;
     private List<Vector2> uvs;
 
     // public
 
     void Awake() {
 
         terrainData = new byte[TERRAIN_WIDTH * TERRAIN_HEIGHT];
         vertices = new List<Vector3>();
         triangles = new List<int>();
         uvs = new List<Vector2>();
 
     }
 
     void Start() {
 
         mesh = GetComponent<MeshFilter>().mesh;
     }
 
     void Update() {
 
         if(rebuildMesh) {
 
             BuildMesh();
 
             rebuildMesh = false;
         }
 
     }
 
     #region Getter and Setter
 
     public void setRebuildFlag() {
         rebuildMesh = true;
     }
 
     public void setTerrainData(int x, int y, byte id) {
 
     }
 
     public byte getTerrainData(int x, int y) {
 
 
         return 0;
     }
 
     #endregion
 
     // private
 
     private void BuildMesh() {
 
         vertices.Clear();
         triangles.Clear();
         uvs.Clear();
 
         int quadCount = 0;
 
         Vector2 texture = new Vector2(0, 30);
 
         for(int x = (int)position.x - (TERRAIN_WIDTH / 2); x < position.x + (TERRAIN_WIDTH / 2); x++) {
             for(int y = (int)position.y - (TERRAIN_HEIGHT / 2); y < position.y + (TERRAIN_HEIGHT / 2); y++) {
 
                 vertices.Add(new Vector3(x, y + 1));
                 vertices.Add(new Vector3(x + 1, y + 1));
                 vertices.Add(new Vector3(x + 1, y));
                 vertices.Add(new Vector3(x, y));
 
                 triangles.Add(quadCount * 4);
                 triangles.Add((quadCount * 4) + 1);
                 triangles.Add((quadCount * 4) + 3);
                 triangles.Add((quadCount * 4) + 1);
                 triangles.Add((quadCount * 4) + 2);
                 triangles.Add((quadCount * 4) + 3);
 
                 uvs.Add(new Vector2(textureUnit * texture.x + textureMargin, textureUnit * texture.y + textureUnit - textureMargin));
                 uvs.Add(new Vector2(textureUnit * texture.x + textureUnit - textureMargin, textureUnit * texture.y + textureUnit - textureMargin));
                 uvs.Add(new Vector2(textureUnit * texture.x + textureUnit - textureMargin, textureUnit * texture.y + textureMargin));
                 uvs.Add(new Vector2(textureUnit * texture.x + textureMargin, textureUnit * texture.y + textureMargin));
 
                 quadCount++;
             }
         }
 
         mesh.vertices = vertices.ToArray();
         mesh.triangles = triangles.ToArray();
         mesh.uv = uvs.ToArray();
     }
 }